Filters having a box casing containing a filtering mass and provided with a wide hook for its suspension from the upper edge of a vertical wall of the aquarium are known. A tube which extends, parallel to the wall, on the inside of the aquarium and dips into the water is connected to the casing. A pump draws the water to be filtered through the tube and passes it through the filtering mass, and returns into the aquarium by passing it over a wide hook, to form a cascade.
A drawback common to most known hang-on filters is that if the electricity supply is interrupted and hence the electrical pump stops, the water contained in the dip tube falls by gravity into the aquarium and, by syphoning, drags with it all the water contained in the filter casing. If, as is generally the case, the water level in the aquarium is below the level of the pump impeller chamber, this chamber empties to unprime the pump, requiring outside action for its re-priming.
To eliminate this drawback, it has already been proposed to form the filter casing as two separate chambers, one of which houses the filtering mass while the other houses the pump impeller (U.S. Pat. No. 4,602,996 to Willinger). The two chambers are separated by a vertical baffle in which one or more small apertures are provided. During normal operation the water drawn by the pump is urged by the impeller into the chamber containing the filtering mass, to pass over the separation baffle between the two and be returned to the aquarium after filteration.
If the electricity supply fails, the impeller chamber rapidly empties by the syphon effect. However, even after this emptying, the water contained in the chamber housing the filtering mass slowly flows through the aperture provided in the vertical baffle and into the impeller chamber. It is no longer transferred into the aquarium because the syphon has been unprimed. Consequently, when the electricity supply returns, the impeller chamber is full of water and the pump can assume regular operation.
This known filter solves the problem of re-priming the pump without requiring external intervention. But, at the same time, it has a low filtering capacity as only a part of the space within the casing houses the filtering mass, the remainder forming the impeller chamber. Consequently, to achieve a filtering capacity equal to that of a filter with a non-self priming pump, the above described filter would have to be considerably larger.
The aquarium taught by Willinger has left and right chambers to house the filter and pump. These chambers have an equal height but the pump only occupies a fraction of the receiving chamber's volume. A great deal of the volume of the chamber is located above the pump and, since it has no filtering element, is unproductive space. Also, if the electricity were to fail, gravity would slowly drain water from the filtering chamber into the receiving chamber only until the level in both chambers were equal. A tube which extends, parallel to the wall, on the inside of the aquarium and dips into the water is connected to the casing. A pump draws the water to filtered through the tube and passes it through the filtering mass, and returns into the aquarium by passing it over a wide hook, to form a cascade.
The main object of the invention is to provide a filter of the initially described type which, besides not producing unpriming of the pump on electricity supply failure, has an overall size substantially equal to that of traditional non-self priming filters.
A further object of the invention is to provide a filter which can be fitted with various accessories and be customized, on the basis of any specific performance required of the aquarium to which it is to be applied.
It is another object of the invention to provide an aquarium filter whose filtering capacity is the majority of the filters chamber's volume. It is also an object of the invention to have a filter whose impeller chamber is as small as possible.